Nowadays, a very wide range of variations and embodiments of mobile radio terminals are available. Some of these mobile radio terminals are not equipped with an antenna socket for connection of an external antenna.
In order to make it possible to operate these mobile radio terminals with an external antenna despite this, antenna couplers are known which allow electromagnetic coupling of RF signals between the antenna coupler and the antenna of the mobile radio terminal.
By way of example, DE 10 037 241 A1 describes a holder for a cellular telephone for installation in a passenger compartment of a motor vehicle, which holder is equipped with a coupling antenna. This coupling antenna allows capacitive coupling of the RF signal between the antenna of the mobile radio terminal and the holder for the cellular telephone when the mobile radio terminal is inserted. A connecting line connects the coupling antenna to an external antenna. The holder for a cellular telephone has an attachment element, for example a magnet, which holds the mobile radio terminal in the holder for a cellular telephone.
In this case, the coupling antenna comprises a dipole structure with an electrical length of λ/4, which is composed of metal or of an electrically highly conductive plastic and is angled. In this case, at least part of the coupling antenna runs in a holding element on the upper face of the holder for a cellular telephone, so that not only are those RF signals which are emitted laterally from the mobile radio antenna injected, but also the RF signals which are emitted upwards. This improves the transmission quality of the RF signals.
DE 19 953 648 A1 describes a modular dual-band planar coupler for coupling an external antenna to a mobile radio terminal. This antenna coupler comprises a conductive plate or foil with a conductive structure which is in the form of a slot, which are composed of one or more conductive waveguide segments in the form of slots, with the inner conductor and the outer conductor of a coaxial waveguide each being conductively connected to the conductive plate or foil on the opposite edges of the slotted conductor. The axis of the inner conductor is in this case guided orthogonally with respect to the normal to the surface of the conductive plate or foil, and at right angles to the axis of the slotted conductor. The structured conductive plate or foil is arranged without making any conductive contact and parallel to the surface of the system-integrated object antenna element and above the antenna element apparatus of the object antenna element.
Furthermore, antenna couplers in the form of coils or metal eyes are known, which are fitted to the antenna of a mobile telephone.
The invention is now based on the object of connecting a mobile radio terminal which is not equipped with an antenna socket to an external antenna, and of keeping the coupling loss as small as possible in the process.